JP2558957B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to an non-aqueous electrolyte secondary battery, relates to a non-aqueous electrolyte secondary battery, especially improved positive electrode.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries having lithium, a lithium alloy or a lithium compound as a negative electrode are expected to have high energy density at high voltage, and many studies have been conducted.

In particular, as the positive electrode active material of these batteries, a substance of the chemical formula shown in (Chemical Formula 2) and the like have been well studied.

[0004]

[Chemical 2] MnO2, TiS ₂

These positive electrode active materials have a potential of about 3 V with respect to Li, but recently, the substances of the chemical formula shown in (Chemical formula 3) and the substances of the chemical formula shown in (Chemical formula 4) show a potential of 4 V or more with respect to Li. It has attracted attention as a positive electrode active material.

[0006]

[Chemical 3] LiMn ₂ O ₄

[0007]

[Chemical 4] LiCoO ₂

That is, efforts have been made to increase the battery voltage as well as the capacity as a means for obtaining a high energy density of the battery.

Of these, the substance represented by (Chemical Formula 4) is considered to be promising as a positive electrode active material because it has a large discharge capacity and may have excellent cycle characteristics.

Further, in order to improve the cycle characteristics, which is one of the important characteristics required for the secondary battery, the complex oxidation represented by the chemical formula shown in (Chemical formula 5) having the substance of the chemical formula shown in (Chemical formula 4) as a skeleton. As a positive electrode active material, improvements have been made to further improve charge / discharge cycle characteristics.

[0011]

Embedded image LiyCo ₁ -xMexO ₂ (Me: Mn, Ni, Cr, 0 ≦ x ≦ 0.5, 0.85 ≦ y ≦ 1.15)

[0012]

By using the above positive electrode active material, a non-aqueous electrolyte secondary battery having a large discharge capacity and excellent cycle characteristics can be realized, but the charging voltage is 4 V.
Therefore, there is a problem that the self-discharge characteristics of the battery after charging are insufficient. The self-discharge of a non-aqueous electrolyte secondary battery is caused by the decomposition of a small amount of water inside the battery and the solvent of the electrolyte solution, which causes problems such as an increase in internal resistance of the battery and a decrease in charge / discharge capacity. In particular, these phenomena become more remarkable as the battery voltage becomes higher, and become more remarkable when stored at high temperature.

Regarding the moisture brought into the battery,
Efforts are being made to suppress the carry-in of water into the inside of the battery by purification such as distillation of the electrolytic solution and drying of the positive electrode active material. However, in the case of a secondary battery that needs to be repeatedly charged and discharged, especially when the charging voltage exceeds 4 V, good self-discharge characteristics cannot be obtained only by removing these water contents.

It is considered that the reaction between the positive electrode active material and the electrolytic solution solvent and the reaction between the material produced by this reaction and the negative electrode lithium are likely to occur, resulting in deterioration of battery performance.

The present invention solves such problems, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having improved self-discharge characteristics.

[0016]

In order to solve this problem, a non-aqueous electrolyte secondary battery of the present invention comprises a lithium, a lithium alloy or a lithium compound negative electrode and a complex oxide represented by the chemical formula shown in (Chemical Formula 5). A positive electrode active material containing a positive electrode active material and a non-aqueous electrolytic solution, in which an alkali metal hydroxide is added to a positive electrode mixture containing the positive electrode active material , and an alkaline metal hydroxide for the positive electrode is used. 100 g of the positive electrode active material
The amount is 0.05 to 0.15 mol.

[0017]

With this configuration, in the non-aqueous electrolyte secondary battery of the present invention, the action of the alkali metal hydroxide inside the non-aqueous electrolyte secondary battery is not clear, but the action is to decompose the organic electrolyte. And the reaction with decomposition products. As a result, it is considered that the deterioration of battery performance, which is considered to be caused by the solvent decomposition product, can be reduced.

[0018]

EXAMPLE A non-aqueous electrolyte secondary battery of one example of the present invention will be described below with reference to the drawings.

Example 1 A battery is manufactured as follows. 3.0 g of acetylene black as a conductive agent was mixed with 100 g of the substance represented by the chemical formula (Chemical Formula 6) as a positive electrode active material, and 1.8 g of lithium hydroxide as an alkali metal hydroxide was added as an aqueous solution and mixed. This mixture was dried at 80 ° C. for 10 hours, and then 4.0 g of polytetrafluoroethylene resin as a binder was mixed to obtain a positive electrode mixture.

[0020]

[Chemical 6] LiCo _0.9 Ni _0.1 O ₂

0.1 gram of positive electrode material mixture having a diameter of 17.5 mm
Was press-molded at 1 ton / cm ² to obtain a positive electrode. A cross-sectional view of the manufactured battery is shown in FIG. The molded positive electrode 1 is placed in the case 2. A porous polypropylene film as the separator 3 was placed on the positive electrode 1. Diameter 1 as negative electrode
A lithium plate 4 having a thickness of 7.5 mm and a thickness of 0.3 mm was pressure-bonded to a sealing plate 5 having a polypropylene gasket 6. A propylene carbonate solution in which 1 mol / l lithium perchlorate was dissolved was used as the non-aqueous electrolyte, and this was added onto the separator 3 and the negative electrode 4. Thereafter, the battery was sealed. The battery obtained as described above is designated as A.

By the same method, B is a battery using a positive electrode to which potassium hydroxide is added, C is a battery using a positive electrode to which sodium hydroxide is added, and a positive electrode to which 0.9 g each of potassium hydroxide and sodium hydroxide is added. Let B be the battery using E, and let E be the battery using the positive electrode to which 0.6 g of lithium hydroxide, potassium hydroxide and sodium hydroxide were added.

As a comparative example, as a battery to which no alkali metal hydroxide was added, a substance 10 of the chemical formula shown in (Chemical Formula 6) was used.
0 g, acetylene black 3.0 g, and polytetrafluoroethylene resin 4.0 g were mixed and used as a positive electrode mixture, and a battery was similarly constructed. This battery is designated as F.

A battery self-discharge test is performed by the following method.
That is, with respect to the battery obtained by the above method, the battery was charged to 4.2 V at a constant current of 1 mA, discharged to 3 V, and after 10 cycles of this charging / discharging, after the 11th cycle of charging, Stored at 60 ° C for 3 weeks.
After storage, it was discharged under the same conditions. Here, the self-discharge rate was defined as follows.

Self-Discharge Rate = (Discharged Electricity at 10th Cycle−Discharged Electricity at 11th Cycle) / 10 Discharged Electricity at 10th Cycle FIG. 1 shows changes in internal resistance of the above batteries due to storage at 60 ° C. Show. In the battery F having the conventional structure, a rapid increase in the internal resistance of the battery was observed immediately after storage, and after 4 weeks, it became 30Ω or more. On the other hand, in the batteries A to E of this example, the increase in the internal resistance of the battery is small, which is about 1/4 that of the battery F.

Further, (Table 1) shows the self-discharge rate of each battery after 3 weeks.

[0027]

[Table 1]

The battery F has a very large self-discharge rate, but in the batteries A to E of this embodiment, it is suppressed within 10%. Thus, the addition of alkali metal hydroxide to the positive electrode has the effect of suppressing self-discharge associated with high temperature storage, and is effective when any of potassium hydroxide, sodium hydroxide, or lithium hydroxide is added. .

Further, the same effect is observed when these alkali metal hydroxides are mixed and added.

Example 2 Further, the amount of lithium hydroxide added to the positive electrode was examined. As the positive electrode active material,
100 g of the chemical compound represented by Chemical formula 7 was used. FIG. 2 shows the relationship between the added amount of lithium hydroxide (the number of moles based on 100 g of the active material) and the internal resistance of the battery using these positive electrodes after storage at 60 ° C. for 3 weeks.

[0031]

[Chemical 7] LiCo _0.9 Mi _0.1 O ₂

From the results, the effect of suppressing the increase of the internal resistance of the battery is recognized when the amount of lithium hydroxide added to the positive electrode is in the range of 0.05 mol to 0.15 mol. Therefore, the amount of lithium hydroxide added to the positive electrode is 100 g of the active material,
The range of 0.05 mol to 0.15 mol is desirable.

Similar results were obtained in the case of potassium hydroxide and sodium hydroxide, and the same effect was observed when the substance having the chemical formula shown in (Chemical Formula 8) was used as the positive electrode active material.

[0034]

Embedded image LiCoO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiCo _0.5 Mn _0.5 , LiCo _0.5 Cr _0.5 O ₂

As described above, in the non-aqueous electrolyte battery using the composite oxide represented by the chemical formula (Chem. 5) as the positive electrode active material, the self-discharge characteristics can be obtained by adding the alkali metal hydroxide to the positive electrode. It is possible to obtain an excellent non-aqueous electrolyte secondary battery.

In the above examples, the electrolyte solution was 1 mol / mol.
This is the result when a propylene carbonate solution in which 1 liter of lithium perchlorate was dissolved was used. Lithium fluoride, propylene carbonate as a solvent,
Electrolytes using carbonates such as ethylene carbonate and esters such as gamma-butyrolactone and methyl acetate were good. However, when ethers such as dimethoxyethane and tetrahydrofuran were used, the self-discharge characteristics were poor, and the improvement of the self-discharge characteristics by adding an alkali metal hydroxide to the positive electrode was not observed. The self-discharge rate was about twice that when propylene carbonate was used. In this example, it is considered that the positive electrode has a voltage of 4 V or higher and the ethers are oxidized.

[0037]

As is apparent from the above description of the embodiments, according to the non-aqueous electrolyte secondary battery of the present invention, the negative electrode of lithium, a lithium alloy or a lithium compound is represented by the chemical formula shown in (Chemical Formula 5). A positive electrode active material using a composite oxide, and a non-aqueous electrolytic solution, the non-aqueous suppressed self-discharge by using a positive electrode mixture containing the positive electrode active material added with an alkali metal hydroxide An electrolyte secondary battery can be obtained, which has great industrial significance.

[Brief description of drawings]

FIG. 1 is a graph showing changes in the internal resistance of the battery of Example 1 of the present invention during storage at 60 ° C.

FIG. 2 is a graph showing the relationship between the amount of lithium hydroxide added (mole number relative to 100 g of active material) of Example 2 of the present invention and the internal resistance of a battery using these positive electrodes after storage at 60 ° C.

FIG. 3 is a vertical sectional view of a coin-type battery used in an example of the present invention.

Claims (2)

(57) [Claims] 1. A negative electrode made of lithium, a lithium alloy or a lithium compound, a positive electrode active material using a composite oxide represented by the chemical formula (formula 1), and a non-aqueous electrolytic solution, and containing the positive electrode active material . A non-aqueous electrolyte secondary battery in which an alkali metal hydroxide is added to the positive electrode mixture . [Chemical formula 1] LiyCo ₁ -xMexO ₂ (Me: Mn, Ni, Cr, 0 ≦ x ≦ 0.5, 0.85 ≦ y ≦ 1.15) 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of the alkali metal hydroxide added to the positive electrode mixture is 0.05 to 0.15 mol per 100 g of the positive electrode active material.